Planck’s primary task is to capture the most ancient light of the cosmos. If this faint light interacts with the hot gas permeating different types of space structures including galaxies and galaxy clusters, its energy distribution is modified in a characteristic way, a phenomenon known as the Sunyaev-Zel’dovich (SZ) effect.

Astronomers have already used the SZ effect to detect galaxy clusters themselves, but it also provides a way to detect faint filaments of gas that might connect one cluster to another.

The presence of hot gas between the billion-light-year-distant clusters Abell 399 and Abell 401 was first hinted at in X-ray data from ESA’s XMM-Newton, and the new data from Planck confirm the observation.

By combining the Planck data with archival X-ray observations from the German satellite Rosat, the astronomers have found temperature of the gas in the bridge to be similar to the temperature of the gas in the two clusters – on the order of 80 million degrees Celsius.